The present invention relates to a screw fluid machine used for air compressors, refrigerators, air conditioners or the like, and more particularly, to a screw fluid machine having a specific rotor profile, wherein a pair of male and female rotors meshed with each other can rotate in a casing and which is suitable, for example, for oil-cooled screw fluid machines such as compressors for supplying oil to a compression space.
A rotor profile is proposed in, for example, Japanese Patent Laid-Open 59-29794, for an oil-cooled screw compressor of the type wherein a male rotor and a female rotor are meshed with each other and one of these rotors drives the other rotor through the direct contact engagement therebetween.
In this conventional fluid machine, a portion of the profile of the driving rotor, which contacts the driven rotor, is limited to one situated around a position where load acting on the contact portions or faces between the rotors is minimized, and the remaining portion of the profile of the driving rotor is maintained so as not to contact the driven rotor by a gap therebetween. Thus, no consideration was given to the fact that the gap was increased in the remaining portion of the profile, since only very limited portions of the rotors meshed with each other.
The profiles of the rotors used in the conventional oil-cooled screw compressor were obtained by merely copying a reference profile with a certain intentionally selected clearance along the entire periphery of the rotors.
In the specification, the reference profile means a profile formed in such a manner that the male and female rotors are meshed with each other without any clearance or gap therebetween.
Thus, in the conventional male and female rotors having the profiles obtained by merely copying the reference profile with a certain clearance along the entire periphery thereof, since motion of a contact point of these rotors deviates from that to be obtained by the fully contacted reference profiles through the revolution, there was uneven or unequal movement of the rotors. Moreover, since there was an unnecessary gap between the rotors, a reduction in efficiency or performance resulted from leakage of compressed air and the like.
As shown in FIG. 3, in a conventional method for providing for rotors, a profile 1 of a male rotor forms a reference profile, with a profile 5 of a female rotor being obtained by copying an essential reference profile thereof with a uniform intentionally selected gap .delta. along the entire periphery thereof in a direction of a center 4 of the female rotor or in a radially inner direction. Arrows in FIG. 3 show directions of rotation of the rotors.
In the male and female rotors thus obtained, there arose problems that the even or uniform movement of the rotors was not ensured as explained above, and, since there was the clearance .delta. between a bottom 5b of the female rotor and a tip 1a of the male rotor, the compressed air leaked as explained above, thus decreasing the efficiency or performance of the machine.